Spyware is a form of a computer virus. Most computers get spyware not through email links but via in-browser downloads. Typically, you would visit a website, click on a link on the website, and then download and install the spyware.
Often, spyware will promise to clean your computer from viruses. To avoid spyware, never download anything from the websites you don’t trust. While it is true that many of the legitimate anti-virus companies offer free anti-virus software, you should only be downloading this software from their websites. Never trust third parties that claim to have free anti-virus tools because in 
reality these tools may turn out to be spyware.
Spyware received its name because of its functions. Some of the spyware viruses spy on what you are typing. Others may try to intercept sensitive private information that you would enter into websites, such as credit card numbers and expiration dates and logins to online banking systems.
Often, spyware will track the websites that you visit with the goal of showing you advertising tailored to your interests. Spyware can also send spam using your computer and your email account, trying to install itself on the computers of your friends.